Field of the Invention
The present disclosure is directed generally to light emitting diodes (LEDs) and more particularly to LED components that can produce a desired light emission profile and these components within a system.
Description of the Related Art
Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
Technological advances over the last decade or more have resulted in LEDs having a smaller footprint, increased emitting efficiency, and reduced cost. LEDs also have an increased operation lifetime compared to other light emitters. For example, the operational lifetime of an LED can be over 50,000 hours, while the operational lifetime of an incandescent bulb is approximately 2,000 hours. LEDs can also be more robust than other light sources and can consume less power. For these and other reasons, LEDs are becoming more popular and are being used in applications that have traditionally been the realm of incandescent, fluorescent, halogen and other emitters. Indeed, lighting applications which previously had typically been served by fixtures using what are known as high intensity discharge (HID) lamps are now being served by LED lighting fixtures. Such lighting applications include, among a good many others, roadway lighting, factory lighting, parking lot lighting, and commercial building lighting.
In many of such products, achieving high levels of illumination over large areas with specific light-distribution requirements is particularly important. One example is fixtures for roadway lighting, an application in which the fixtures are generally placed along roadway edges while light distribution is desired along a significant portion of roadway length and, of course, on the roadway itself—generally to the exclusion of significant light off the roadway. And in such situations it is desirable to minimize the use of large complex reflectors and/or varying orientations of multiple light sources to achieve desired illumination patterns.
LEDs are also being used in displays, both big and small. Large screen LED based displays (often referred to as giant screens) are becoming more common in many indoor and outdoor locations, such as at sporting events, race tracks, concerts and in large public areas, such as Times Square in New York City.
Additionally, LEDs are being used in a variety of lighting applications. Some lighting applications require uniform ambient lighting, whereas others require particular beam shapes, emission profiles, or intensity levels. One example of such a use includes street lighting, which requires uniform light output of a particular intensity in a particular beam shape to allow for illumination of only a particular area.
Present technology utilizes optics and geometries that maximize light extraction from the LED to obtain uniform emission profiles. This usually entails a hemispherical lens coupled to a light emitting element where the optical centers of the lens and the emitting surface are perfectly aligned, and the peak light emission is along the optical axis. However, such a configuration may not be advantageous for all situations, such as when an LED display is mounted above the viewer's eye level or a directed lighting pattern is required, for example in street lighting.
Referring now to FIGS. 1A and 1B, exemplary LED downlights 10 are shown mounted at an elevated point above a street 12, functioning as a street light. The street 12 area to be lit is typically positioned below the downlight 10 and is at an angle with respect to the downlight's emission direction, which is perpendicular to the downlight surface. When light emission is required at an angle other than the center, as shown in FIG. 1A, light is wasted because secondary optics must be used to redirect the light and secondary optics cause some percentage of loss. FIG. 1A shows unmodified emission pattern. FIG. 1B shows a modified emission pattern using secondary optics. The LED downlight street light as shown in FIG. 1A includes a plurality of emitters, such as an LED package, which may include an LED mounted within the street light housing. Secondary optics must be placed over these LED packages to modify the emission pattern from that shown in FIG. 1A to the pattern shown in FIG. 1B. FIG. 2 shows an exemplary LED package 200, which may be used in the street lights of FIGS. 1A-1B. The LED package 200 includes an array of LED chips 215 on a substrate 205, with a lens 200. As shown, the center CA of the array of LED chips 215 is aligned with the center CL of the lens 220. The peak emission for the LED package 200 is along the package's longitudinal axis. FIG. 3 is a polar iso-candelar graph 30 for the LED package 200, showing the peak emission along the emitter's longitudinal axis.
FIG. 1A shows a light fixture 10 comprising a plurality of LED packages 200 emitting with characteristics that display a peak emission directed along a perpendicular direction. The intensity profile (Iv) and far field pattern (FFP) peak emission characteristics for the downlight 10 are also perpendicular to the fixture along the perpendicular axis.
One way to reduce the amount of light that is wasted is by mounting the light emitters at an angle to better match the desired illumination area or viewer's line of sight, but this can require complex and expensive mounting configurations or hardware that is difficult to use. Efforts have also been made to control the light emission from LED packages by modifying the shape of the encapsulant or lens, but this may require special, costly lens tooling and complex lens fabrication processes. Some systems may utilize secondary optics to alter beam profiles or redirect light patterns to different angles; however, the secondary optics may cause significant losses on the order of 10-12% and add cost to the display system.